Method of dual EPI process for semiconductor device

ABSTRACT

The present disclosure provides a method of fabricating a semiconductor device that includes forming first and second gate structures over first and second regions of a substrate, respectively, forming spacers on sidewalls of the first and second gate structures, the spacers being formed of a first material, forming a capping layer over the first and second gate structures, the capping layer being formed of a second material different from the first material, forming a protection layer over the second region to protect the second gate structure, removing the capping layer over the first gate structure; removing the protection layer over the second region, epitaxially (epi) growing a semiconductor material on exposed portions of the substrate in the first region, and removing the capping layer over the second gate structure by an etching process that exhibits an etching selectivity of the second material to the first material.

PRIORITY DATA

This application claims priority to Provisional Application Ser. No.61/303,853 filed on Feb. 12, 2010, the entire disclosure of which isincorporated herein by reference.

BACKGROUND

When a semiconductor device such as a metal-oxide-semiconductorfield-effect transistors (MOSFETs) is scaled down through varioustechnology nodes, high-k dielectric material and metal are adopted toform a gate stack. In addition, strained source/drain features have beenimplemented using epitaxial (epi) silicon germanium (SiGe) to enhancecarrier mobility and improve device performance in p-type devices.Further, raised source/drain features have been implemented using episilicon (Si) in n-type devices. However, current techniques to performdual epi process for n-type and p-type devices have not beensatisfactory in all respects. For example, voids may be formed betweenthe gate structure and the strained source/drain features duringprocessing which can degrade device performance.

SUMMARY

An embodiment of the present invention involves a method of fabricatinga semiconductor device. The method includes forming first and secondgate structures over first and second regions of a substrate,respectively; forming spacers on sidewalls of the first and second gatestructures, the spacers being formed of a first material; forming acapping layer over the first and second gate structures, the cappinglayer being formed of a second material different from the firstmaterial; forming a protection layer over the second region to protectthe second gate structure; removing the capping layer over the firstgate structure; removing the protection layer over the second region;epitaxially (epi) growing a semiconductor material on exposed portionsof the substrate in the first region; and removing the capping layerover the second gate structure by an etching process that exhibits anetching selectivity of the second material to the first material.

Another embodiment of the present invention involves a method offabricating a semiconductor device. The method includes forming firstand second gate structures over first and second regions of a substrate,respectively; forming spacers on sidewalls of the first and second gatestructures; forming a first capping layer over the first and second gatestructures; forming a first protection layer over the second region toprotect the second gate structure; removing the first capping layer overthe first gate structure; removing the first protection layer over thesecond region; epitaxially (epi) growing a first semiconductor materialon exposed portions of the substrate in the first region; removing thefirst capping layer over the second gate structure by wet etching,wherein the wet etching selectively etches the first capping layer butnot the spacers disposed on the sidewalls of the first gate structure;forming a second capping layer over the first and second gatestructures; forming a second protection layer over the first region toprotect the first gate structure; removing the second capping layer overthe second gate structure; forming a recess in the substrate at eitherside of the second gate structure; removing the second protection layerover the first gate structure; and epitaxially growing a secondsemiconductor material to fill the recess.

Yet another embodiment of the present invention involves a method offabricating a semiconductor device. The method includes forming firstand second gate structures over first and second regions of a substrate,respectively; forming spacers on sidewalls of the first and second gatestructures; forming a first capping layer over the first and second gatestructures; forming a second capping layer over the first capping layer;forming a first protection layer over the second region to protect thesecond gate structure; removing the first and second capping layers overthe first gate structure; removing the first protection layer over thesecond region; epitaxially (epi) growing silicon on exposed portions ofthe substrate in the first region; removing the first and second cappinglayers over the second gate structure by wet etching, wherein the wetetching selectively removes the first and second capping layers but notthe spacers disposed on the sidewalls of the first gate structure;forming a third capping layer over the first and second gate structures;forming a fourth capping layer over the third capping layer; forming asecond protection layer over the first region to protect the first gatestructure; removing the third and fourth capping layers over the secondgate structure; etching a recess in the substrate at either side of thesecond gate structure; removing the second protection layer over thefirst region; epitaxially (epi) growing silicon germanium (SiGe) to fillthe recess; and removing the third and fourth capping layers over thefirst gate structure by wet etching, wherein the wet etching selectivelyremoves the third and fourth capping layers but not the spacers disposedon the sidewalls of the second gate structure.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIGS. 1A-1B illustrate a flow chart of a method of fabricating asemiconductor device with a dual epitaxial (epi) process according tovarious aspects of the present disclosure;

FIGS. 2-11 illustrate cross-sectional views of a semiconductor device atvarious stages of fabrication according to the method of FIGS. 1A-1B;

FIGS. 12A-12B illustrate a flow chart of another method of fabricating asemiconductor device with a dual epi process according to variousaspects of the present disclosure;

FIGS. 13-24 illustrate cross-sectional views of a semiconductor deviceat various stages of fabrication according to the method of FIGS.12A-12B;

FIG. 25 illustrates a flow chart of still another method of fabricatinga semiconductor device with a dual epi process according to variousaspects of the present disclosure; and

FIGS. 26-33 illustrate cross-sectional views of a semiconductor deviceat various stages of fabrication according to the method of FIG. 25.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof various embodiments. Specific examples of components and arrangementsare described below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a first feature over or on a second featurein the description that follows may include embodiments in which thefirst and second features are formed in direct contact, and may alsoinclude embodiments in which additional features may be formedinterposing the first and second features, such that the first andsecond features may not be in direct contact.

Referring to FIG. 1, illustrated is a flowchart of a method 100 offabricating a semiconductor device with a dual epitaxial (epi) processaccording to various aspects of the present disclosure. The method 100begins with block 102 in which a semiconductor substrate having firstand second regions is provided. The method 100 continues with block 104in which first and second gate structures are formed over the first andsecond regions of the substrate, respectively. The method 100 continueswith block 106 in which a first capping layer is formed over the firstand second regions including the first and second gate structures. Themethod continues with block 108 in which a second capping layer isformed over the first capping layer. The method 100 continues with block110 in which a first protection layer is formed over the second regionto protect the second gate structure. The method 100 continues withblock 112 in which portions of the first and second capping layers areremoved in the first region. The remaining portions of the first andsecond capping layer are disposed on the sidewalls of the first gatestructure. The method 100 continues with block 114 in which the firstprotection layer over the second region is removed.

The method 100 continues with block 116 in which a first semiconductormaterial is epitaxially grown on exposed portions of the substrate inthe first region. The method 100 continues with block 118 in which thefirst capping layer over the second gate structure is removed. Themethod 100 continues with block 120 in which a third capping layer isformed over the first and second regions of the substrate. The method100 continues with block 122 in which a second protection layer isformed over the first region to protect the first gate structure. Themethod 100 continues with block 124 in which portions of the third andsecond capping layers are removed in the second region. The remainingportions of the third and second capping layers are disposed on thesidewalls of the second gate structure. The method 100 continues withblock 126 in which a recess is formed in the substrate at either side ofthe second gate structure. The method 100 continues with block 128 inwhich the second protection layer over the first region is removed. Themethod 100 continues with block 130 in which the third capping in thefirst region is removed, and the remaining portions of the third andsecond capping layers in the second region are removed. The method 100continues with block 132 in which fabrication of the semiconductordevice is completed. The discussion that follows illustrates variousembodiments of a semiconductor device that can be fabricated accordingto the method 100 of FIG. 1.

Referring FIGS. 2-11, illustrated are cross-sectional views of asemiconductor device 200 at various stages of fabrication according tothe method 100 of FIG. 1. It should be noted that the semiconductordevice 200 may be fabricated by CMOS technology. Accordingly, additionalprocesses may be provided before, during, and after the method 100 ofFIGS. 1A-1B, and that some process are only briefly described herein. Itis understood that FIGS. 2-11 have been simplified for the sake ofclarity to better understand the inventive concepts of the presentdisclosure. In FIG. 2, the semiconductor device 200 includes a substrate202. The substrate 202 includes a silicon substrate. In anotherembodiment, the semiconductor substrate 202 may include an epitaxiallayer. For example, the substrate 202 may have an epitaxial layeroverlying a bulk semiconductor. The substrate 202 further includes dopedregions such as p-wells and n-wells. Furthermore, the substrate 202 mayinclude a semiconductor-on-insulator (SOI) structure such as a burieddielectric layer. Alternatively, the substrate 202 may include a burieddielectric layer such as a buried oxide (BOX) layer, such as that formedby a method referred to as separation by implantation of oxygen (SIMOX)technology, wafer bonding, selective epitaxial growth (SEG), or otherproper method. The semiconductor device 200 includes active regionsdefined in the substrate 202.

Various shallow trench isolation (STI) structures are formed in thesemiconductor substrate for isolating the various active regions. Theformation of STI may include etching a trench in a substrate and fillingthe trench by insulator materials such as silicon oxide, siliconnitride, or silicon oxynitride. The filled trench may have a multi-layerstructure such as a thermal oxide liner layer with silicon nitridefilling the trench. In one embodiment, the STI structure may be createdusing a process sequence such as: growing a pad oxide, forming a lowpressure chemical vapor deposition (LPCVD) nitride layer, patterning anSTI opening using photoresist and masking, etching a trench in thesubstrate, optionally growing a thermal oxide trench liner to improvethe trench interface, filling the trench with CVD oxide, using chemicalmechanical planarization (CMP) to etch back, and using nitride strippingto leave the STI structure.

One or more operational devices are formed in the active regions. Theoperational devices include n-type and p-type metal-oxide-semiconductordevices (NMOS and PMOS). The NMOS and PMOS devices may be fabricated byCMOS technology processing. The NMOS and PMOS devices may include planarfield-effect transistor (FET) devices 206, 208 and non-planar transistordevices such as FinFET devices 210, 212. It is understood that bothtypes of transistors are illustrated for the sake of example, and thatthe FinFET devices 210, 212 are shown across a fin structure whereas theFET devices 206, 208 are shown across a gate structure. The FinFETdevices 210, 212 include fins 214 that extend from the substrate 202.Although only one fin is shown for the NMOS and PMOS devices 210, 212,it is understood that the number of fins may vary depending on theparticular application. The fins 214 n, 214 p may be fabricated by usingsuitable process such as photolithography and etch. For example, thephotolithography process may include forming a photoresist layer(resist) overlying the substrate (e.g., on a silicon layer), exposingthe resist to a pattern, performing post-exposure bake processes, anddeveloping the resist to form a masking element including the resist.The masking element may then be used to etch fins 214 n, 214 p from thesubstrate 202. The fins 214 n, 214 p may be etched using reactive ionetch (RIE) and/or other suitable processes. Shallow trench isolation(STI) structures 215 surround the fins 214 n, 214 p and isolate each finfrom the other fins. The fins 214 n, 214 p may extend beyond the STI 215at a distance ranging from about 300 to about 400 Angstrom (Å). The STIstructures 215 may include any suitable insulating material.

In the present embodiment, each NMOS and PMOS devices 206, 208, 210, 212includes a gate structure formed on the semiconductor substrate 202. Itis understood that the FinFET devices 210, 212 may include more than onegate structure in multi-gate configurations. Although not shown, thegate structures wrap around the fins 214 n, 214 p allowing gate controlof the channel from both sides of the fin. Further, the gate structure(not shown) of the FinFET devices 210, 212 may be similar to the gatestructure of the FET devices 208, 206 except that the cross-section viewwould be along the fin 214 n, 214 p.

The gate structure includes a gate dielectric 216 and a gate electrode218. The gate dielectric 216 may include silicon oxide, silicon nitride,high-k dielectric, or other suitable material. The high-k dielectriclayer may include a binary or ternary high-k film such as HfOx.Alternatively, the high-k dielectric layer 216 may optionally includeother high-k dielectrics such as LaO, AlO, ZrO, TiO, Ta2O5, Y2O3, SrTiO3(STO), BaTiO3 (BTO), BaZrO, HfZrO, HfLaO, HfSiO, LaSiO, AlSiO, HfTaO,HfTiO, (Ba,Sr)TiO3 (BST), Al2O3, Si3N4, oxynitrides, or other suitablematerials. The gate dielectric is formed by a suitable process such asan atomic layer deposition (ALD), chemical vapor deposition (CVD),physical vapor deposition (PVD), thermal oxidation, UV-ozone oxidation,or combinations thereof.

The gate electrode 218 may include polysilicon (or poly). For example,silane (SiH₄) may be used as a chemical gas in a CVD process to form thepoly. The poly layer may include a thickness ranging from about 600 toabout 800 angstrom (Å). The gate structure may further include a hardmask layer 220 formed on the gate electrode 218. The hard mask layer 220includes silicon oxide. Alternatively, the hard mask layer 220 mayoptionally silicon nitride, silicon oxynitride, and/or other suitabledielectric materials, and may be formed using a method such as CVD orPVD. The hard mask layer 220 may include a thickness ranging from about100 to about 400 angstrom (Å).

The semiconductor device 200 includes a sealing layer 222 formed on eachsidewall of the gate structures. The sealing layer 222 includes siliconnitride and has a thickness ranging from about 5 to about 8 nm. Thesealing layer 222 may be formed by CVD, PVD, ALD, plasma enhanced CVD(PECVD), or other suitable technique. In some embodiments, an ionimplantation process may be performed to form lightly doped source/drainregions (LDD) in the substrate 202. The LDD regions (not shown) arealigned with the sidewall of the gate structure. The ion implantationprocess may utilize p-type dopants (e.g., B or In) for the PMOS devicesand n-type dopants (P or As) for the NMOS devices.

An capping layer such as an oxide layer 224 is formed over the substrate202 including over the gate structures and fins 214 n, 214 p. The oxidelayer 224 may be formed by CVD, PVD, ALD, or other suitable technique.The oxide layer 224 includes a thickness ranging from about 3 nm toabout 5 nm. In the present embodiment, the oxide layer 224 has athickness of about 4 nm. Another capping layer such as a silicon nitridelayer 226 is formed over the oxide layer 224. The nitride layer 226 maybe formed by CVD, PVD, ALD, furnace-type processing, or other suitabletechnique. The silicon nitride layer 226 includes a thickness rangingfrom about 20 to about 30 nm. In the present embodiment, the nitridelayer 226 has a thickness of about 25 nm.

In FIG. 3, a patterned photoresist layer 230 is formed to protect thePMOS devices 208, 212. The patterned photoresist layer 230 may be formedby a photolithography process. An exemplary photolithography process mayinclude processing steps of photoresist coating, soft baking, maskaligning, exposing, post-exposure baking, developing photoresist, andhard baking. The photolithography exposing process may also beimplemented or replaced by other proper techniques such as masklessphotolithography, electron-beam writing, ion-beam writing, and molecularimprint. In some embodiments, a bottom anti-reflective coating (BARC)layer 232 may be formed prior to forming the resist layer 230.

In FIG. 4, an etching process is performed to remove portions of thenitride layer 226 directly overlying the substrate 202 at either side ofthe gate structure of the NMOS device 206. It is noted that the nitridelayer 226 over the fin 214 n is completely removed due to the heightdifference between the gate structure and the fin. Further, the BARClayer 232 overlying the NMOS devices 206, 210 may be removed during theetching process. The patterned photoresist layer 230 protects the oxidelayer 224 and the nitride layer 226 overlying the PMOS devices 208, 212during the etching process. In the present embodiment, the etchingprocess includes a dry etching process that utilizes a gas combinationof CHxFy/O2 or SF6/CHxFy/He (where x=1 to 3 and y=4−x) or other suitablegas. With respect to the gas combination of CHxFy/O2, the dry etchingprocess utilizes a pressure ranging from about 1 mT to about 1000 mT, apower ranging from about 500 W to about 3000 W, a bias voltage rangingfrom about 100 V to about 500 V, a CHxFy flow rate ranging from about 10sccm to about 500 sccm, and an O2 flow rate ranging from about 10 sccmto about 500 sccm. With respect to the gas combination of SF6/CHxFy/He,the dry etching process utilizes a pressure ranging from about 1 mT toabout 1000 mT, a power ranging from about 500 W to about 3000 W, a biasvoltage ranging from about 0 V to about 200 V, a SF6 flow rate rangingfrom about 10 sccm to about 100 sccm, a CHxFy flow rate ranging fromabout 10 sccm to about 500 sccm, and an He flow rate ranging from about10 sccm to about 1000 sccm.

Following the etching process, spacers 234 are formed on the sidewallsof the gate structures of the NMOS device 206. The spacers 234 includeportions of the nitride layer 226 and oxide layer 224. In the presentembodiment, the spacers 234 have a critical dimension of about 15 nm.Further, portions of the oxide layer 224 are exposed in the NMOS devices206, 210 after the etching process.

In FIG. 5, an etching process is performed to remove exposed portions ofthe oxide layer 224 in the NMOS devices 206, 210. The etching processincludes a wet etching process, dry etching process, or combination dryand wet etching processes to remove portions of the silicon substrate202 that are exposed. For example, the wet etching may include an HF dipto remove the exposed portions of the oxide layer 224 in the NMOSdevices 206, 210. It is noted that the nitride layer 226 protects theoxide layer 226 overlying the PMOS devices 208, 212. An epitaxial (epi)process is performed to grow epi silicon on exposed portions of thesilicon substrate to form raised source/drain features. The photoresistlayer 230 and BARC layer 232 protecting the PMOS devices 208, 212 areremoved prior to the epi process. It is understood that epi process isknown in the art and thus not described in detail herein. In the presentembodiment, epi silicon 240 is formed on source/drain regions of theNMOS device 206, and epi silicon 240 is formed on the fin 214 n of theNMOS device 210. In some other embodiments, a trench may be formed inthe substrate 202 at the source/drain regions and in the fin 214 n, andsilicon carbide (SiC) may be deposited in the trench to form strainedfeatures for exerting stress (e.g., tensile strain) on a channel regionof the NMOS devices 208, 210.

In FIG. 6, an etching process is performed to remove the nitride layer226 overlying the PMOS devices 208, 212. The etching process includes awet etching utilizing H3PO4 or other suitable etchant. The wet etchingis selected so that a slow etch rate is achieved to protect the poly. Itis noted that the wet etching also removes the nitride layer of thespacers 234 thereby forming a gap 242 between the sidewall of the gatestructure and the epi silicon 240.

In FIG. 7, a capping layer such as a silicon nitride layer 246 is formedover the substrate 202. The nitride layer 246 may be formed by CVD, PVD,ALD, furnace-type processing, or other suitable technique. The siliconnitride layer 226 includes a thickness ranging from about 20 to about 30nm. In the present embodiment, the nitride layer 226 has a thickness ofabout 25 nm. It has been observed that voids may form within the gap 242between the sidewall of the gate structure and the epi silicon 240 afterformation of the nitride layer 246 which can adversely affect subsequentprocessing. As such, the epi process may be tuned so that the episilicon 240 can have a desired profile to minimize the risk of voidsbeing formed between the gate structure and the epi silicon 240.

In FIG. 8, a patterned photoresist layer 250 is formed to protect theNMOS devices 206, 210. The patterned photoresist layer 250 may be formedby a photolithography process. An exemplary photolithography process mayinclude processing steps of photoresist coating, soft baking, maskaligning, exposing, post-exposure baking, developing photoresist andhard baking. The photolithography exposing process may also beimplemented or replaced by other proper techniques such as masklessphotolithography, electron-beam writing, ion-beam writing, and molecularimprint. In some embodiments, a bottom anti-reflective coating (BARC)layer 252 may be formed prior to forming the resist layer 250.

In FIG. 9, an etching process is performed to remove portions of thenitride layer 246 overlying the substrate 202 at either side of the gatestructure of the PMOS devices 208, 212. It is noted that the nitridelayer 246 over the fin 214 p is completely removed due to the heightdifference between the gate structure and the fin. Further, the BARClayer 252 overlying the PMOS devices 208, 212 may be removed during theetching process. The etching process may be similar the one discussedabove with reference to FIG. 4. The patterned photoresist layer 250protects the nitride layer 246 overlying the NMOS devices 206, 210during the etching process. Following the etching process, spacers 254are formed on the sidewalls of the gate structures of the PMOS devices208, 212. The spacers 254 include portions of the nitride layer 246 andoxide layer 224. In the present embodiment, the spacers 234 have acritical dimension of about 15 nm. Further, portions of the oxide layer224 are exposed in the PMOS devices 208, 212 after the etching process.Those portions of the oxide layer 224 may be removed by an HF dip orother suitable etching process thereby exposing portions of thesubstrate 202 and fin 214 p of the PMOS devices 208, 212.

Another etching process is performed to form a recess 256 in thesubstrate 202 of the PMOS device 208, and a recess 258 in the fin 214 pof the PMOS device 212. The etching process may include dry etching, wetetching, or combination thereof. In the present embodiment, the etchingprocess includes a dry etching process that utilizes a combination ofHBr/Cl2/O2/He, a pressure ranging from about 1 mT to about 1000 mT, apower ranging from about 50 W to about 1000 W, a bias voltage rangingfrom about 100 V to about 500 V, an HBr flow rate ranging from about 10sccm to about 500 sccm, a Cl2 flow rate ranging from about 0 sccm toabout 500 sccm, an O2 flow rate ranging from about 0 sccm to about 100sccm, and an He flow rate ranging from about 0 sccm to about 1000 sccm.The dry etching removes portions of the silicon substrate 202 and fin214 p that are unprotected or exposed. Accordingly, the recess 256 hasvertical sidewalls that are aligned with the spacers 254 due to thedirectional/anisotropic etching. The recess 256, 258 may have a depthranging from about 400 to about 800 Angstrom (Å). In some embodiments, apre-cleaning process may be performed to clean the recess 256, 258 withHF or other suitable solution.

In FIG. 10, a semiconductor material is deposited in the recess 256, 258to form strained structures of the PMOS devices 208, 212. In anembodiment, an epitaxial (epi) process is performed to deposit asemiconductor material in the recess 256, 258. The semiconductormaterial is different from the substrate 202. Accordingly, the channelregion of the PMOS device 208, 212 is strained/stressed (e.g.,compressive strain) to enable carrier mobility of the device and enhancedevice performance. The patterned photoresist 250 and BARC layer 252protecting the NMOS devices 206, 210 are removed prior to the epiprocess. In the present embodiment, silicon germanium (SiGe) isdeposited by an epi process in the recess 256, 258 of the substrate 202and the fin 214 p to form SiGe features 260 in a crystalline state. TheSiGe epi process is known in the art, and thus not described in detailherein. It is noted that the nitride layer 246 protects the NMOS devices206, 210 during the SiGe epi process. Additionally, the SiGe 260 isdeposited such that it is raised above the surface of the substrate 202.In some embodiments, the SiGe 260 may be in-situ doped with p-typeimpurities, such as B or In, to form source/drain regions of the PMOSdevices 208, 212.

In FIG. 11, an etching process is performed to remove the nitride layer246 overlying the NMOS devices 206, 210. The etching process includes awet etching utilizing H3PO4 or other suitable etchant. The wet etchingis selected so that a slow etch rate is achieved to protect the poly. Asdiscussed above, the gap 242 between the sidewalls of the gate structureand the epi silicon 240 of the NMOS device 206 may induce voids beingformed during subsequent processing. Further, it is noted that the wetetching also removes the nitride layer of the spacers 254 therebyforming a gap 262 between the sidewalls of the gate structure and theepi SiGe 260 of the PMOS device 208. As such, the gap 262 may alsoinduce voids being formed during subsequent processing similar to thegap 242 in the NMOS device 206. The discussion that follows illustratesanother embodiment of a dual epitaxial (epi) process that minimizes therisk of voids being formed between the gate structure and the strainedsource/drain features.

The semiconductor device 200 continues with processing to completefabrication as discussed briefly below. For example, source/drainregions for the NMOS devices 206, 210 may be formed by ion implantationof n-type dopants such as P or As, and source/drain regions for the PMOSdevices 208, 212 may be formed by ion implantation of p-type dopantssuch as B. Additionally, silicide features are formed on the raisedsource/drain regions to reduce the contact resistance. The silicide canbe formed on the source and drain regions by a process includingdepositing a metal layer, annealing the metal layer such that the metallayer is able to react with silicon to form silicide, and then removingthe non-reacted metal layer.

An inter-level dielectric (ILD) layer is formed on the substrate and achemical mechanical polishing (CMP) process is further applied to thesubstrate to planarize the substrate. Further, an contact etch stoplayer (CESL) may be formed on top of the gate structures before formingthe ILD layer. In an embodiment, the gate electrode 208 remains poly inthe final device. In another embodiment, the poly is removed andreplaced with a metal in a gate last or gate replacement process. In agate last process, the CMP process on the ILD layer is continued toexpose the poly of the gate structures, and an etching process isperformed to remove the poly thereby forming trenches. The trenches arefilled with a proper work function metal (e.g., p-type work functionmetal and n-type work function metal) for the PMOS devices and the NMOSdevices.

A multilayer interconnection (MLI) including metal layers andinter-metal dielectric (IMD) is formed on the substrate to electricallyconnect various device features to form a integrated circuit. Themultilayer interconnection includes vertical interconnects, such asconventional vias or contacts, and horizontal interconnects, such asmetal lines. The various interconnection features may implement variousconductive materials including copper, tungsten and silicide. In oneexample, a damascene process is used to form copper multilayerinterconnection structure.

Referring to FIGS. 12A-12B, illustrated is a flowchart of a method 300of fabricating a semiconductor device with a dual epitaxial (epi)process according to various aspects of the present disclosure. Themethod 300 begins with block 302 in which a semiconductor substratehaving first and second regions is provided. The method 300 continueswith block 304 in which first and second gate structures are formed overthe first and second regions of substrate, respectively. The method 300continues with block 306 in which spacers are formed on the sidewalls ofthe first and second gate structures. The method 300 continues withblock 308 in which a first capping layer is formed over the first andsecond regions of the substrate including the first and second gatestructures. The method 300 continues with block 310 in which a firstprotection layer is formed over the second region to protect the secondgate structure. The method 300 continues with block 312 in which a firstsemiconductor material is epitaxially grown on exposed portions of thesubstrate in the first region. The method 300 continues with block 314in which the first capping layer over the second gate structure isremoved.

The method 300 continues with block 316 in which a second capping layeris formed over the first and second regions of the substrate includingthe first and second gate structures. The method 300 continues withblock 318 in which a second protection layer is formed over the firstregion to protect the first gate structure. The method 300 continueswith block 320 in which the second capping layer over the second gatestructure is removed. The method 300 continues with block 322 in which arecess is formed in the substrate at either side of the second gatestructure. The method 300 continues with block 324 in which the secondprotection layer over the first gate structure is removed. The method300 continues with block 326 in which a second semiconductor material isepitaxially grown to fill the recess. The method 300 continues withblock 328 in which fabrication of the semiconductor device is completed.The discussion that follows illustrates various embodiment of asemiconductor device that can be fabricated according to the method 300of FIGS. 12A-12B.

Referring to FIGS. 13-24, illustrated are cross-sectional views of asemiconductor device 400 at various stages of fabrication according tothe method 300 of FIGS. 12A-12B. It should be noted that thesemiconductor device 400 may be fabricated by CMOS technology.Accordingly, additional processes may be provided before, during, andafter the method 300 of FIGS. 12A-12B, and that some process are onlybriefly described herein. Further, the semiconductor device 400 issimilar to the semiconductor device 200 of FIGS. 2-11, and thus similarfeatures are numbered the same for the sake of clarity and simplicity.In FIG. 13, the semiconductor device 400 includes a substrate 202. Thesubstrate 202 includes a silicon substrate. In another embodiment, thesemiconductor substrate 202 may include an epitaxial layer. For example,the substrate 202 may have an epitaxial layer overlying a bulksemiconductor. The substrate 202 further includes doped regions such asp-wells and n-wells.

Various shallow trench isolation (STI) structures are formed in thesemiconductor substrate for isolating the various active regions. Theformation of STI may include etching a trench in a substrate and fillingthe trench by insulator materials such as silicon oxide, siliconnitride, or silicon oxynitride. The filled trench may have a multi-layerstructure such as a thermal oxide liner layer with silicon nitridefilling the trench. In one embodiment, the STI structure may be createdusing a process sequence such as: growing a pad oxide, forming a lowpressure chemical vapor deposition (LPCVD) nitride layer, patterning anSTI opening using photoresist and masking, etching a trench in thesubstrate, optionally growing a thermal oxide trench liner to improvethe trench interface, filling the trench with CVD oxide, using chemicalmechanical planarization (CMP) to etch back, and using nitride strippingto leave the STI structure.

One or more operational devices are formed in the active regions. Theoperational devices include n-type and p-type metal-oxide-semiconductordevices (NMOS and PMOS). The NMOS and PMOS devices may be fabricated byCMOS technology processing. The NMOS and PMOS devices may include planarfield-effect transistor (FET) devices 206, 208 and non-planar transistordevices such as FinFET devices 210, 212. It is understood that bothtypes of transistors are illustrated for the sake of example, and thatthe FinFET devices 210, 212 are shown across a fin structure whereas theFET devices 206, 208 are shown across a gate structure. The FinFETdevices 210, 212 include fins 214 n, 214 p that extend from thesubstrate 202. Although only one fin is shown for the NMOS and PMOSdevices 210, 212, it is understood that the number of fins may varydepending on the particular application.

In the present embodiment, each NMOS and PMOS devices includes a gatestructure formed on the semiconductor substrate 202. It is understoodthat the FinFET devices 210, 212 may include more than one gatestructure in multi-gate configurations. Although not shown, the gatestructures wrap around the fins 214 n, 214 p allowing gate control ofthe channel from both sides of the fin. The gate structure includes agate dielectric 216 and a gate electrode 218. The gate structure mayfurther include a hard mask layer 220 formed on the gate electrode 218.

The semiconductor device 400 includes a sealing layer 222 formed on eachsidewall of the gate structures. The sealing layer 222 includes siliconnitride and has a thickness ranging from about 5 to about 8 nm. In thepresent embodiment, the sealing layer 222 has a thickness of about 7 nm.The sealing layer 222 may be formed by CVD, PVD, ALD, plasma enhancedCVD (PECVD), or other suitable technique. In some embodiments, an ionimplantation process may be performed to form lightly doped source/drainregions (LDD) in the substrate 202. The LDD regions (not shown) arealigned with the sidewall of the gate structure. The ion implantationprocess may utilize p-type dopants (e.g., B or In) for the PMOS devicesand n-type dopants (P or As) for the NMOS devices.

A spacer-material layer such as a silicon nitride layer 402 is formedover the substrate 202 including over the gate structures and fins 214n, 214 p. The silicon nitride layer 402 may be formed by CVD, PVD, ALD,or other suitable technique. In the present embodiment, the siliconnitride layer 402 includes a thickness ranging from about 4 nm to about6 nm. In an embodiment, the silicon nitride layer 402 has a thickness ofabout 5 nm. Further, the silicon nitride layer 402 is doped with carbonso that an etching rate is different from undoped silicon nitride aswill be explained in detail below.

In FIG. 14, an etching process is performed on the silicon nitride layer402 to form spacers 404. It is noted that the silicon nitride layer 402overlying the fins 214 n, 214 p is completely removed due to the heightdifference between the gate structures and the fins. Following theetching process, the spacers 404 are disposed on the sidewalls of thegate structures of the NMOS device 206 and PMOS device 208. The combinedthickness of the sealing layer 222 and the spacer 404 is about 12 nm.

In FIG. 15, a capping layer such as an oxide layer 406 is formed overthe substrate 202 including over the gate structures and fins 214 n, 214p. The oxide layer 406 may be formed by CVD, PVD, ALD, or other suitabletechnique. The oxide layer 406 includes a thickness ranging from about 3nm to about 5 nm. In the present embodiment, the oxide layer 406 has athickness of about 4 nm. Another capping layer such as a silicon nitridelayer 408 is formed over the oxide layer 406. The silicon nitride layer408 may be formed by CVD, PVD, ALD, furnace-type processing, or othersuitable technique. The silicon nitride layer 408 includes a thicknessranging from about 4 to about 6 nm. In the present embodiment, thesilicon nitride layer 408 has a thickness of about 5 nm. Further, thesilicon nitride layer 408 is not doped with carbon as compared to thedoped silicon nitride of the spacers 404.

In FIG. 16, a patterned photoresist layer 420 is formed to protect thePMOS devices 208, 212. The patterned photoresist layer 420 may be formedby a photolithography process. An exemplary photolithography process mayinclude processing steps of photoresist coating, soft baking, maskaligning, exposing, post-exposure baking, developing photoresist andhard baking. The photolithography exposing process may also beimplemented or replaced by other proper techniques such as masklessphotolithography, electron-beam writing, ion-beam writing, and molecularimprint. In some embodiments, a bottom anti-reflective coating (BARC)layer may be formed prior to forming the resist layer 420.

In FIG. 17, an etching process is performed to remove the nitride layer408 overlying the NMOS devices 206, 210. The patterned photoresist layer420 protects the silicon nitride layer 408 overlying the PMOS devices208, 212 during the etching process. In the present embodiment, theetching process includes a dry etching process, wet etching process, orcombination thereof. The etching process may stop at the oxide layer 404overlying the NMOS devices 206, 210. An etching process is performed toremove the oxide layer 406 overlying the NMOS devices 206, 210. Theetching process includes a wet etching process, dry etching process, orcombination thereof to remove portions. For example, the wet etching mayinclude an HF dip to remove the oxide layer 406 overlying the NMOSdevices 206, 210. It is noted that the silicon nitride layer 408protects the PMOS devices 208, 212 during the wet etching. The patternedphotoresist 420 is removed following the etching process therebyexposing portions of the substrate 202 and the fin 214 n of the NMOSdevices 206, 210.

In FIG. 18, an epitaxial (epi) process is performed to grow epi siliconon exposed portions of the silicon substrate and silicon fin 214 n. Itis understood that epitaxial process is known in the art and thus notdescribed in detail herein. In the present embodiment, epi silicon 430is formed on source/drain regions of the NMOS device 206, and episilicon 430 is formed on the fin 214 n of the NMOS device 210. Further,it is noted that the epi silicon 430 is formed adjacent the spacers 404in the NMOS device 206.

In FIG. 19, an etching process is performed to remove the nitride layer408 overlying the PMOS devices 208, 212. The etching process includes adry etching process, wet etching process, or combination thereof. Theetching process may stop at the oxide layer 404 overlying the PMOSdevices 208, 212. It is noted that the spacers 404 on the gate structureof the NMOS device 206 are not removed due to high etching selectivitybetween the doped silicon nitride and undoped silicon nitride. As such,no gap is formed between the gate structure and the epi silicon 430, andthus the risk of voids being formed in subsequent processing isminimized. An etching process is performed to remove the oxide layer 406overlying the PMOS devices 208, 212. The etching process includes a wetetching process, dry etching process, or combination thereof to removeportions. For example, the wet etching may include an HF dip to removethe oxide layer 406 overlying the PMOS devices 208, 212.

In FIG. 20, a capping layer such as an oxide layer 434 is formed overthe substrate 202 including over the gate structures, fins 214 n, 214 p,and the epi silicon 430. The oxide layer 434 may be formed by CVD, PVD,ALD, or other suitable technique. The oxide layer 434 includes athickness ranging from about 3 nm to about 5 nm. In the presentembodiment, the oxide layer 434 has a thickness of about 4 nm. Anothercapping layer such as a silicon nitride layer 436 is formed over theoxide layer 434. The silicon nitride layer 436 may be formed by CVD,PVD, ALD, furnace-type processing, or other suitable technique. Thesilicon nitride layer 436 includes a thickness ranging from about 4 toabout 6 nm. In the present embodiment, the silicon nitride layer 436 hasa thickness of about 5 nm. Further, the silicon nitride layer 436 is notdoped with carbon as compared to the silicon nitride of the spacers 404.

In FIG. 21, a patterned photoresist layer 440 is formed to protect theNMOS devices 206, 210. The patterned photoresist layer 440 may be formedby a photolithography process. An exemplary photolithography process mayinclude processing steps of photoresist coating, soft baking, maskaligning, exposing, post-exposure baking, developing photoresist andhard baking. The photolithography exposing process may also beimplemented or replaced by other proper techniques such as masklessphotolithography, electron-beam writing, ion-beam writing, and molecularimprint. In some embodiments, a bottom anti-reflective coating (BARC)layer may be formed prior to forming the resist layer 440.

In FIG. 22, an etching process is performed to remove the nitride layer436 overlying the PMOS devices 208, 212. The etching process includes adry etching process, wet etching process, or combination thereof. Theetching process may stop at the oxide layer 434 overlying the PMOSdevices 208, 212. Another etching process is performed to remove theoxide layer 434 overlying the PMOS devices 208, 212. The etching processincludes a wet etching process, dry etching process, or combinationthereof to remove portions. For example, a wet etching may include an HFdip to remove the oxide layer 434 overlying the PMOS devices 208, 212.The patterned photoresist layer 440 protects the silicon nitride layer436 overlying the NMOS devices 206, 210 during the etching processes.

An etching process is performed to form a recess 456 in the substrate202 of the PMOS device 208, and a recess 458 in the fin 214 p of thePMOS device 212. The etching process may include a dry etching, wetetching, or combination thereof. In the present embodiment, the etchingprocess includes a dry etching process that utilizes a combination ofHBr/Cl2/O2/He, a pressure ranging from about 1 mT to about 1000 mT, apower ranging from about 50 W to about 1000 W, a bias voltage rangingfrom about 100 V to about 500 V, an HBr flow rate ranging from about 10sccm to about 500 sccm, a Cl2 flow rate ranging from about 0 sccm toabout 500 sccm, an O2 flow rate ranging from about 0 sccm to about 100sccm, and an He flow rate ranging from about 0 sccm to about 1000 sccm.The dry etching removes portions of the silicon substrate 202 and fin214 p that are unprotected or exposed. Accordingly, the recess 456 hasvertical sidewalls that are aligned with the spacers 404 due to thedirectional/anisotropic etching. The recess 456, 458 may have a depthranging from about 400 to about 800 Angstrom (Å). In some embodiments, apre-cleaning process may be performed to clean the recess 456, 458 withHF or other suitable solution.

In FIG. 23, a semiconductor material is deposited in the recess 456, 458to form strained structures of the PMOS devices 208, 212. In anembodiment, an epitaxial (epi) process is performed to deposit asemiconductor material in the recess 456, 458. The semiconductormaterial is different from the substrate 202. Accordingly, the channelregion of the PMOS device 208, 212 is strained/stressed (e.g.,compressive strain) to enable carrier mobility of the device and enhancedevice performance. The patterned photoresist 440 protecting the NMOSdevices 206, 210 is removed prior to the epi process. In the presentembodiment, silicon germanium (SiGe) is deposited by an epi process inthe recess 456, 458 of the substrate 202 and the fin 214 p to form SiGefeatures 460 in a crystalline state. The SiGe epi process is known inthe art, and thus not described in detail herein. The SiGe 460 is formedadjacent the spacers 404 in the PMOS device 208. Further, it is notedthat the nitride layer 436 protects the NMOS devices 206, 210 during theSiGe epi process. Additionally, the SiGe 460 is deposited such that itis raised above the surface of the substrate 202. In some embodiments,the SiGe 460 may be in-situ doped with p-type impurities, such as B orIn, to form source/drain regions of the PMOS devices 208, 212.

In FIG. 24, an etching process is performed to remove the nitride layer436 and oxide layer 434 overlying the NMOS devices 206, 210. The etchingprocess includes a wet etching utilizing H3PO4 or other suitableetchant. It is noted that the spacers 404 of the PMOS device 206 are notremoved due to high etching selectivity between the doped siliconnitride and undoped silicon nitride. As such, no gap is formed betweenthe gate structure and the epi SiGe 460, and thus the risk of voidsbeing formed in subsequent processing is minimized. The semiconductordevice 200 continues with processing to complete fabrication as wasdiscussed above with reference to semiconductor device 200.

Referring to FIG. 25, illustrated is a flowchart of a method 500 offabricating a semiconductor device with a dual epitaxial (epi) processaccording to various aspects of the present disclosure. The method 500begins with block 502 in which a semiconductor substrate having firstand second regions is provided. The method 500 continues with block 504in which first and second gate structures are formed over the first andsecond regions of substrate, respectively. The method 500 continues withblock 506 in which first spacers are formed on the sidewalls of thefirst and second gate structures. The first spacers have a first etchrate. The method 500 continues with block 508 in which a first etchingis performed on the substrate. The method 500 continues with block 510in which a first semiconductor is epitaxially grown on exposed portionsof the substrate. The method 500 continues with block 512 in which acapping layer is formed over the substrate and the first and second gatestructures. The capping layer having a second etch rate greater than thefirst etch rate. The method 500 continues with block 514 in which a maskis formed to protect the first region of the substrate.

The method 500 continues with block 516 in which an unprotected portionof the capping layer overlying the second region is removed. The method500 continues with block 518 in which the mask is removed. The method500 continues with block 520 in which a second etching is performed onthe substrate. The method 500 continues with block 522 in which a secondsemiconductor material is epitaxially grown on exposed portions of thesubstrate. The method 500 continues with block 524 in which a remainingportion of the capping layer over the first region is removed. Themethod 500 continues with block 526 in which fabrication of thesemiconductor device is completed. The discussion that followsillustrates various embodiment of a semiconductor device that can befabricated according to the method 500 of FIG. 25

Referring to FIGS. 26-33, illustrated are cross-sectional views of asemiconductor device 600 at various stages of fabrication according tothe method 500 of FIG. 25. It should be noted that the semiconductordevice 600 may be fabricated by CMOS technology. Accordingly, additionalprocesses may be provided before, during, and after the method 500 ofFIG. 25, and that some process are only briefly described herein. InFIG. 26, the semiconductor device 600 includes a substrate 602. Thesubstrate 602 includes a silicon substrate. In another embodiment, thesemiconductor substrate 602 may include an epitaxial layer. For example,the substrate 602 may have an epitaxial layer overlying a bulksemiconductor. The substrate 602 further includes doped regions such asp-wells and n-wells.

Various shallow trench isolation (STI) structures 610 are formed in thesemiconductor substrate 602 for isolating the various active regions.The formation of STI may include etching a trench in a substrate andfilling the trench by insulator materials such as silicon oxide, siliconnitride, or silicon oxynitride. The filled trench may have a multi-layerstructure such as a thermal oxide liner layer with silicon nitridefilling the trench. In one embodiment, the STI structure may be createdusing a process sequence such as: growing a pad oxide, forming a lowpressure chemical vapor deposition (LPCVD) nitride layer, patterning anSTI opening using photoresist and masking, etching a trench in thesubstrate, optionally growing a thermal oxide trench liner to improvethe trench interface, filling the trench with CVD oxide, using chemicalmechanical planarization (CMP) to etch back, and using nitride strippingto leave the STI structure.

One or more operational devices are formed in the active regions. Theoperational devices include n-type and p-type metal-oxide-semiconductordevices (NMOS and PMOS). The NMOS and PMOS devices may be fabricated byCMOS technology processing. The NMOS and PMOS devices may includefield-effect transistor (FET) devices. In the present embodiment, theNMOS device 606 and PMOS device 608 each includes a gate structureformed on the semiconductor substrate 602. The gate structure is similarto the gate structures disclosed above in the planar NMOS and PMOSdevices. The gate structure includes a gate dielectric 616 and a gateelectrode 618. The gate structure may further include a hard mask layer620 formed on the gate electrode 618.

The semiconductor device 600 may include a sealing layer (not shown)formed on each sidewall of the gate structures. The sealing layerincludes silicon nitride and has a thickness ranging from about 5 toabout 8 nm. The sealing layer may be formed by CVD, PVD, ALD, plasmaenhanced CVD (PECVD), or other suitable technique. In some embodiments,an ion implantation process may be performed to form lightly dopedsource/drain regions (LDD) in the substrate 602. The LDD regions (notshown) are aligned with the sidewall of the gate structure. The ionimplantation process may utilize p-type dopants (e.g., B or In) for thePMOS devices and n-type dopants (P or As) for the NMOS devices.

The semiconductor device 600 includes spacers 624 formed on sidewalls ofthe gate structures. The spacers 624 are formed by depositing adielectric layer and performing an dry etching (anisotropic etching) onthe dielectric layer. In the present embodiment, the spacers 624 areformed of a silicon nitride layer doped with carbon (SiCN). The carbonconcentration may range from about 1% to about 50%. In one embodiment,the carbon concentration is 6%. In other embodiments, the carbonconcentration is 10%. The carbon concentration may vary depending on adesired etch rate with respect to a wet etch solution, such as HF,H3PO4, and SPM as will be explained in detail below. The carbon dopedsilicon nitride layer may be formed by CVD, LPCVD, PECVD, PVD, ALD, orother suitable technique. The spacers 624 may have a thickness rangingfrom about 5 nm (50 angstrom) to about 15 nm (150 angstrom).

An etching process 626 is performed on exposed portions of the substrate602. The etching process 626 may include a dry etching, wet etching, orcombination thereof. The etching process 626 forms recesses in thesubstrate 602.

In FIG. 27, an epitaxial (epi) process is performed to grow epi siliconon exposed portions of the silicon substrate 602. It is understood thatepitaxial process is known in the art and thus not described in detailherein. In the present embodiment, epi silicon 630 is formed onsource/drain regions of the NMOS device 606, and epi silicon 631 isformed on at either side of the gate structure of the PMOS device 608.

In FIG. 28, a capping layer 632 such as a boron doped silicon nitride(SiBN) or boron nitride (BN) is formed over the substrate 202 includingover the gate structures of the NMOS 606 and PMOS 608 devices. The boronconcentration may range from about 1% to about 50%. The dopingconcentration may be selected to achieved a desired etch rate withrespect to a wet etch solution, such as HF, H3PO4, and SPM. In thepresent embodiment, the desired wet etch rate of the capping layer 632is not less than 5 times the wet etch rate of the spacers 624. In anembodiment, the etch rate of the capping layer 632 is 16 times (16×) theetch rate of the spacers 624 with respect to HF. In other embodiments,the etch rate of the capping layer 632 is 50 times (50×) the etch rateof the spacers 624 with respect to H3PO4. In still other embodiments,the etch rate of the capping layer 632 is 60 times (60×) the etch rateof the spacers 624 with respect to SPM. The capping layer 632 may have athickness ranging from about 8 nm (80 angstrom) to about 15 nm (150angstrom).

A patterned photoresist layer 634 is formed to protect a portion of thecapping layer 632 overlying the NMOS device 606. The patternedphotoresist layer 634 may be formed by a photolithography process. Anexemplary photolithography process may include processing steps ofphotoresist coating, soft baking, mask aligning, exposing, post-exposurebaking, developing photoresist and hard baking. The photolithographyexposing process may also be implemented or replaced by other propertechniques such as maskless photolithography, electron-beam writing,ion-beam writing, and molecular imprint. In some embodiments, a bottomanti-reflective coating (BARC) layer may be formed prior to forming theresist layer 634.

In FIG. 29, an etching process is performed to remove an unprotectedportion of the capping layer 632 overlying the PMOS device 608. Thepatterned photoresist layer 634 protects the capping layer 632 aoverlying the NMOS device 606. In the present embodiment, the etchingprocess includes a dry etching process, wet etching process, orcombination thereof. The etching process may stop at the epi silicon631. Accordingly, the spacers 624 (SiCN) of the gate structure of thePMOS device 608 are exposed.

In FIG. 30, the patterned photoresist 634 is removed following theetching process. In FIG. 31, an etching process is performed to form arecess 644 in the substrate 602 of the PMOS device 608. The etchingprocess may include a dry etching, wet etching, or combination thereof.In the present embodiment, the etching process includes a dry etchingprocess that utilizes a combination of HBr/Cl2/O2/He, a pressure rangingfrom about 1 mT to about 1000 mT, a power ranging from about 50 W toabout 1000 W, a bias voltage ranging from about 100 V to about 500 V, anHBr flow rate ranging from about 10 sccm to about 500 sccm, a Cl2 flowrate ranging from about 0 sccm to about 500 sccm, an O2 flow rateranging from about 0 sccm to about 100 sccm, and an He flow rate rangingfrom about 0 sccm to about 1000 sccm. The dry etching removes portionsof the silicon substrate 602 that are unprotected or exposed.Accordingly, the recess 644 has vertical sidewalls that are aligned withthe spacers 624 due to the directional/anisotropic etching. The recess644 may have a depth ranging from about 400 to about 800 Angstrom (Å).In some embodiments, a pre-cleaning process may be performed to cleanthe recess 644 with HF or other suitable solution.

In FIG. 32, a semiconductor material is deposited in the recess 644 toform strained structures of the PMOS device 608. In an embodiment, anepitaxial (epi) process is performed to deposit a semiconductor materialin the recess 644. The semiconductor material is different from thesubstrate 602. Accordingly, the channel region of the PMOS device 608 isstrained/stressed (e.g., compressive strain) to enable carrier mobilityof the device and enhance device performance. In the present embodiment,silicon germanium (SiGe) is deposited by an epi process in the recess644 of the substrate 602 to form SiGe features 650 in a crystallinestate. The SiGe epi process is known in the art, and thus not describedin detail herein. The SiGe 650 is formed adjacent the spacers 624 in thePMOS device 608. Further, it is noted that the capping layer 632 aprotects the NMOS device 606 during the SiGe epi process. Additionally,the SiGe 650 is deposited such that it is raised above the surface ofthe substrate 602. In some embodiments, the SiGe 650 may be in-situdoped with p-type impurities, such as B or In, to form source/drainregions of the PMOS device 608.

In FIG. 33, an etching process is performed to remove the capping layer632 a overlying the NMOS device 606. The etching process includes a wetetching utilizing HF, H3PO4, or SPM other suitable etchant. It is notedthat the spacers 624 of the PMOS device 608 are substantially notremoved due to high etching selectivity between the capping layer 632 a(SiBN or BN) and spacers 624 (SiCN). As such, critical dimension (CD)variation will be minimized which results in less CESL damage duringdummy poly removal (less gate length variation), improved deviceperformance (less variation in Ion and Ioff), and reduced risk ofcontact (source/drain) to poly short leakage. The semiconductor device600 continues with processing to complete fabrication as was discussedabove with reference to semiconductor device 200.

The semiconductor devices 200, 400, 600 serve only as examples. Thesemiconductor devices 200, 400, 600 may be used in various applicationssuch as digital circuit, imaging sensor devices, a hetero-semiconductordevice, dynamic random access memory (DRAM) cell, a single electrontransistor (SET), and/or other microelectronic devices (collectivelyreferred to herein as microelectronic devices). Of course, aspects ofthe present disclosure are also applicable and/or readily adaptable toother type of transistor, including single-gate transistors, double-gatetransistors, and other multiple-gate transistors, and may be employed inmany different applications, including sensor cells, memory cells, logiccells, and others.

The foregoing has outlined features of several embodiments. Thoseskilled in the art should appreciate that they may readily use thepresent disclosure as a basis for designing or modifying other processesand structures for carrying out the same purposes and/or achieving thesame advantages of the embodiments introduced herein. Those skilled inthe art should also realize that such equivalent constructions do notdepart from the spirit and scope of the present disclosure, and thatthey may make various changes, substitutions and alterations hereinwithout departing from the spirit and scope of the present disclosure.

What is claimed is:
 1. A method of fabricating a semiconductor device,comprising: forming first and second gate structures over first andsecond regions of a substrate, respectively; forming spacers onsidewalls of the first and second gate structures, the spacers beingformed of a first material that is doped; forming a capping layer overthe first and second gate structures, the capping layer being formed ofa second material different from the first material, wherein the secondmaterial is undoped; forming a protection layer over the second regionto protect the second gate structure; removing the capping layer overthe first gate structure; removing the protection layer over the secondregion; epitaxially (epi) growing a semiconductor material on exposedportions of the substrate in the first region; and removing the cappinglayer over the second gate structure by an etching process that exhibitsan etching selectivity of the second material that is undoped to thefirst material that is doped, wherein removing the capping layer overthe second gate structure by the etching process that exhibits theetching selectivity of the second material that is undoped to the firstmaterial that is doped occurs prior to forming another capping layerover the second gate structure, the another capping layer being formedof the second material.
 2. The method of claim 1, wherein the firstmaterial comprises silicon nitride doped with carbon.
 3. The method ofclaim 2, wherein the second material comprises silicon nitride not dopedwith carbon.
 4. The method of claim 1, further comprising: prior toforming the capping layer over the first and second gate structures,forming an oxide layer over the first and second gate structures; priorto removing the protection layer over the second region, removing theoxide layer over the first gate structure; and after epi growing thesemiconductor material, removing the oxide layer over the second gatestructure by wet etching, wherein the wet etching selectively etches theoxide layer but not the first material of the spacers disposed on thesidewalls of the first gate structure.
 5. The method of claim 1, whereinthe epi growing the semiconductor material forms raised source and drainfeatures at either side of the first gate structure.
 6. The method ofclaim 1, further comprising thereafter: forming another capping layerover the first and second gate structures, the another capping layerbeing formed of the second material; forming another protection layerover the first region to protect the first gate structure; removing theanother capping layer over the second gate structure; etching a recessin the substrate at either side of the second gate structure, the recesshaving sides aligned with the spacers disposed on the sidewalls of thesecond gate structure; removing the another protection layer over thefirst region; epitaxially growing another semiconductor material to fillthe recess; and removing the another capping layer over the first gatestructure by the etching process that exhibits the etching selectivityof the second material layer to the first material.
 7. The method ofclaim 6, further comprising: prior to forming the another capping layerover the first and second gate structures, forming an oxide layer overthe first and second gate structures; prior to removing the anotherprotection layer over the first region, removing the oxide layer overthe second gate structure; and after epi growing the anothersemiconductor material, removing the oxide layer over the first gatestructure by wet etching, wherein the wet etching selectively etches theoxide layer but not the first material of the spacers disposed on thesidewalls of the second gate structure.
 8. The method of claim 6,wherein the semiconductor material includes silicon (Si) and wherein theanother semiconductor material includes silicon germanium (SiGe).
 9. Themethod of claim 6, wherein the first gate structure is part of an NMOSdevice and wherein the second gate structure is part of a PMOS device.10. The method of claim 1, further comprising etching a recess in thesubstrate adjacent the second gate structure; and epitaxially growinganother semiconductor material to fill the recess.
 11. A methodcomprising: forming first and second gate structures over first andsecond regions of a substrate, respectively; forming spacers onsidewalls of the first and second gate structures, the spacers beingformed of a first material; forming a capping layer over the first andsecond gate structures, the capping layer being formed of a secondmaterial different from the first material; forming a protection layerover the second region to protect the second gate structure; removingthe capping layer over the first gate structure; removing the protectionlayer over the second region; epitaxially (epi) growing a semiconductormaterial on exposed portions of the substrate in the first region;removing the capping layer over the second gate structure by an etchingprocess that exhibits an etching selectivity of the second material tothe first material, after removing the capping layer, forming anothercapping layer over the first and second gate structures, the anothercapping layer being formed of the second material; removing the anothercapping layer over the second gate structure; and epitaxially (epi)growing another semiconductor material on exposed portions of thesubstrate in the second region.
 12. The method of claim 11, furthercomprising removing the another capping layer over the first gatestructure by the etching process that exhibits the etching selectivityof the second material layer to the first material.
 13. The method ofclaim 11, wherein epitaxially (epi) growing the second semiconductormaterial on exposed portions of the substrate in the second regionincludes: etching a recess in the substrate at either side of the secondgate structure; and epitaxially growing another semiconductor materialto fill the recess.
 14. The method of claim 13, wherein the recesshaving sides aligned with the spacers disposed on the sidewalls of thesecond gate structure.
 15. The method of claim 11, further comprisingforming another protection layer over the another capping layer in thefirst region prior to removing the another capping layer over the secondgate structure.
 16. The method of claim 15, removing the protectionlayer over the first gate structure prior to epitaxially (epi) growinganother semiconductor material on exposed portions of the substrate inthe second region.
 17. A method comprising: forming first and secondgate structures over first and second regions of a substrate,respectively; forming spacers on sidewalls of the first and second gatestructures, the spacers being formed of a doped first material; forminga capping layer over the first and second gate structures, the cappinglayer being formed of a undoped second material; forming a protectionlayer over the second region to protect the second gate structure;removing the capping layer over the first gate structure; removing theprotection layer over the second region; epitaxially (epi) growing asemiconductor material on exposed portions of the substrate in the firstregion; removing the capping layer over the second gate structure by anetching process that exhibits an etching selectivity of the undopedsecond material to the doped first material; after removing the cappinglayer, forming another capping layer over the first and second gatestructures, the another capping layer being formed of the secondmaterial; removing the capping layer over the second gate structure; andepitaxially (epi) growing another semiconductor material on exposedportions of the substrate in the second region.
 18. The method of claim17, further comprising forming first and second fins in the first andsecond regions of the substrate, respectively.
 19. The method of claim17, wherein the undoped second material of the capping layer includes asilicon nitride layer disposed over the silicon oxide layer; and whereinthe doped first material of the spacers includes silicon nitride dopedwith carbon.
 20. The method of claim 17, wherein forming spacers onsidewalls of the first and second gate structures includes formingperforming an etching process to form the spacers, and wherein formingthe capping layer over the first and second gate structures occurs afterperforming the etching process to form the spacers.